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encoding/asn1: string type tags are not documented to work in Unmarshal #42570

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mjg59 opened this issue Nov 12, 2020 · 4 comments
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encoding/asn1: string type tags are not documented to work in Unmarshal #42570

mjg59 opened this issue Nov 12, 2020 · 4 comments
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Documentation FrozenDueToAge help wanted NeedsFix The path to resolution is known, but the work has not been done.
Milestone
Go1.16

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@mjg59
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mjg59 commented Nov 12, 2020 •
edited by FiloSottile

What version of Go are you using (go version)?

1.14

Does this issue reproduce with the latest release?

Yes

What operating system and processor architecture are you using (go env)?

linux amd64

What did you do?

I have the following struct:

type ComponentIdentifierV2 struct {
        ComponentClass           ComponentClass
        ComponentManufacturer    string
        ComponentModel           string
        ComponentSerial          string                `asn1:"optional,tag:0"`
        ComponentRevision        string                `asn1:"optional,tag:1"`
        ComponentManufacturerID  int                   `asn1:"optional,tag:2"`
        FieldReplaceable         bool                  `asn1:"optional,tag:3"`
        ComponentAddresses       []ComponentAddress    `asn1:"optional,tag:4"`
        ComponentPlatformCert    CertificateIdentifier `asn1:"optional,tag:5"`
        ComponentPlatformCertURI string                `asn1:"optional,tag:6"`
        Status                   asn1.Enumerated       `asn1:"optional,tag:7"`
}

Note that ComponentRevision is tag:1, so context specific. The fact that it's a string means that getUniversalType() will return PrintableString, and this will not be overridden because there's no explicit tag type in the encoded stream.

The spec definition of this struct is:

ComponentIdentifier ::= SEQUENCE {
componentClass ComponentClass,
componentManufacturer UTF8String (SIZE (1..STRMAX)),
componentModel UTF8String (SIZE (1..STRMAX)),
componentSerial[0] IMPLICIT UTF8String (SIZE (1..STRMAX)) OPTIONAL,
componentRevision [1] IMPLICIT UTF8String (SIZE (1..STRMAX)) OPTIONAL,
componentManufacturerId [2] IMPLICIT PrivateEnterpriseNumber OPTIONAL,
fieldReplaceable [3] IMPLICIT BOOLEAN OPTIONAL,
componentAddresses [4] IMPLICIT SEQUENCE(SIZE(1.. MAX)) OF ComponentAddress OPTIONAL
componentPlatformCert [5] IMPLICIT CertificateIdentifier OPTIONAL,
componentPlatformCertUri [6] IMPLICIT URIReference 
}

ie, componentRevision is a UTF8String, not a PrintableString. The certificate I'm parsing has an @ sign in, which is legitimate in a UTF8String but not a PrintableString. Since we have no explicit information in the stream to treat this as a UTF8String we continue treating it as a PrintableString, and then fail because of the "invalid" character.

What did you expect to see?

A string containing an @ sign.

What did you see instead?

asn1: syntax error: PrintableString contains invalid character
@mjg59
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mjg59 commented Nov 12, 2020

This actually works if I do:

asn1:"utf8,optional,tag:1"

which is documented as doing something in Marshal() but not in Unmarshal().

@mjg59 mjg59 changed the title encoding/asn1 doesn't let me specify the expected type of a string encoding/asn1 doesn't document string types in unmarshal() Nov 12, 2020
@FiloSottile FiloSottile added Documentation help wanted NeedsFix The path to resolution is known, but the work has not been done. labels Nov 12, 2020
@FiloSottile FiloSottile added this to the Go1.16 milestone Nov 12, 2020
@FiloSottile FiloSottile changed the title encoding/asn1 doesn't document string types in unmarshal() encoding/asn1: string type tags are not documented to work in Unmarshal Nov 12, 2020
@ericchiang
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I can take the documentation fix

imxyb added a commit to imxyb/go that referenced this issue Nov 13, 2020
@imxyb
Fixes golang#42570
48e36b7 
encoding/ans1: add utf8 tag doc for Unmarshal method.
imxyb added a commit to imxyb/go that referenced this issue Nov 13, 2020
@imxyb
Fixes golang#42570
21a4992 
encoding/asn1: add utf8 tag doc for Unmarshal method.
@imxyb imxyb mentioned this issue Nov 13, 2020
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@gopherbot
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Change https://golang.org/cl/269777 mentions this issue: encoding/asn1: add utf8 tag doc for Unmarshal method.

@gopherbot
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Change https://golang.org/cl/269798 mentions this issue: encoding/asn1: document unmarshaling behavior for IMPLICIT string fields

@golang golang locked and limited conversation to collaborators Jan 12, 2022
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encoding/asn1: add utf8 tag doc for Unmarshal method. imxyb/go
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@FiloSottile @mjg59 @ericchiang @gopherbot